1. Field of the Invention
The present invention relates to a novel spinal fixation device. More particularly the present invention relates to a novel one-piece device configured to bilaterally secure two vertebrae together in a manner that increases the stability and strength of the connection between the vertebrae. Also provided is a spinal fixation system by which a first spinal fixation device according to the present invention can be secured to a second spinal fixation device in such a manner so as to provide for two or more sequentially aligned vertebra to be securely attached one to the other. A method of securing two or more vertebrae one to the other is also disclosed.
2. Background of the Technology
The biomechanics and strength of facet screws and translaminar facet screws have been studied extensively. In addition, numerous clinical studies of these devices have also been reported. Facet screws have been used in a very limited manner for spinal fixation in the United States. Facet screws and translaminar facet screws have seen limited use in spine surgery, being primarily applied as an adjuvant to anterior interbody grafts. When employed in this fashion they serve as a posterior tension band by locking the facet joint. Facet screws are therefore extremely straightforward in application. However, the concern with their use is the limited fixation and rigidity that they are able to provide. To improve on this deficiency, translaminar facet screws have been advocated. Further, the use of translaminar facet screws provided improved strength through purchase into the cortical aspect of the lamina and the spinous process prior to entering the facet joint. However, the risk for dural laceration and nerve injury increases dramatically when this device is used as compared to the use of a regular facet screw. In addition, the angle of application is such that a longer or separate incision must be made far lateral and a trocar must be placed in a blind fashion through significant spinal musculature. For these reasons, the surgical application of the translaminar facet screw can be very challenging.
Alternatively, the use of pedicle screws has been demonstrated to be a very rigid and reliable means of spinal fixation. In fact, it is possible that many pedicle screw spinal fixation systems are too rigid and, as a result, stress shield the fusion area. Moreover, the application of pedicle screws in spinal fixation can have many potential pitfalls. Since the pedicle cannot be directly visualized, multiple methods have been developed to locate the pedicle and apply the screw in the appropriate location, with the proper angulation, and the correct superior/inferior trajectory. Use of anatomic landmarks is helpful in making such application, but it is by no means perfect. Even the most skilled surgeons can be misled by aberrant anatomy. Even in straightforward anatomical situations, pedicles can have various diameters and significant variations in trajectory exist within the normal bell curve of the population. For these reasons, imaging is used by many surgeons to facilitate the surgical application of pedicle screws. Various intra-operative imaging modalities exist including fluoroscopy, flouroscan, and CT-image guidance. The former imparts significant radiation to the surgical team while the latter two incur significant cost and increased operating room time. All three modalities increase surgical time, potentially increase infection rate, and incur cost.
Furthermore, the surgical application of screws takes significant time. In addition, when screws are applied prior to decortication of the lateral gutters and application of bone graft, the screws often decrease the visualization of the gutters necessary for proper preparation. Further, the upper numbered screw many times has to be placed extremely close to, if not through, a facet joint that is not involved in fusion. This additional intrusion may, in the future, result in pain secondary to facet irritation. As an example of such additional and unwanted intrusion, in an L4-L5 fusion procedure, the L4 screw is placed at the level of the L3-4 facet joint. Finally, inappropriate or inaccurate pedicle screw placement can lead to disastrous consequences. For example, if a screw is misplaced, the resulting breakout of the pedicle can incur nerve root irritation, dural laceration, and spinal cord injury if above the L1-L2 region, and disc space disruption, and potential vascular damage if placed too far anterior.
Because of the great concern over misplaced pedicle screws, intraoperative imaging is necessarily used as stated above. In addition, for safety reasons neurological monitoring of somatosensory evoked potentials and EMG stimulation of the screws are used by many surgeons. The imaging and monitoring incur significant additional costs for the surgical procedure.
A need therefore exists for a spinal fixation device and method that provides improvements over conventional devices in the attachment of two vertebra to each other with reduced risk to the patient, less surgical time, cost and trouble to apply and dependably strong security of attachment.
In an attempt to decrease the risk and cost associated with the application of pedicle screws, an alternative form of fixation over that conventionally used has been devised: the facet triangle device. The device of the present invention is a simple concept that is easy, quick, safe, and cost-effective to use. Further, the facet triangle device provides a rigid construct in one, two, and more level lumbar fusions.